Almost one third of all infants are not or cannot be breast-fed and receive infant formula. Formula-feeding significantly increases the risk to develop necrotizing enterocolitis (NEC), the most frequent and most lethal disorder in neonates. We hypothesize that oligosaccharides present in human milk but not in infant formula contribute to the protective effects in breast-fed infants by inhibiting P-selectin mediated neutrophil adhesion and activation, which are key events in NEC pathogenesis. To test this hypothesis, the PI will continue his training in glycobiology and receive additional intensive training in gastroenterology with a special emphasis on neonatal NEC. The PI will be strongly supported by his Career Development Training Committee, consisting of world-leading experts in their respective fields. The PI's scientific background, together with the additional training of this award, will bring novel ideas and innovative perspectives for an independent scientific career, which will benefit medical research on human infant nutrition, health and disease. Besides receiving intensive glycobiology and gastroenterology training, the PI will be trained in a rat model of NEC, learning how to induce and assess onset, progression and outcome of the disease. AIM 1 uses this model to assess whether human milk oligosaccharides in general reduce NEC incidence and severity. AIM 2 will use Frontal Affinity Chromatography Mass Spectrometry to identify individual milk oligosaccharides with high affinity for P-selectin and chemically synthesize them in sufficient amounts to be tested in vitro and in vivo. AIM 3 will then assess the effects of these oligosaccharides on P-selectin-mediated neutrophil adhesion and activation in in vitro parallel flow chamber models and ex vivo whole blood assays. AIM 4 will return to the rat model of NEC and assess the effects of these individual oligosaccharides in intervention studies. We aim to identify bioactive human milk oligosaccharides lacking from infant formula that inhibit key events in NEC pathogenesis. Our results, combined with interdisciplinary training, will guide intervention studies that assess the effectiveness of individual milk oligosaccharides on reducing the risk of NEC in human neonates. Our studies will support the efforts to provide formula-fed infants with the same benefits that breast-fed infants receive with their mother's milk.